Radio-frequency (RF) antennas are ubiquitously employed for transmitting RF signals from a wide range of devices. The signal radiation characteristics of an RF antenna is often determined by the type of application in which the RF antenna is used. For example, a radio station or a cellular signal broadcasting system would typically use an RF antenna having an omnidirectional signal radiation characteristic so as to provide signal coverage over a wide area all around the antenna. However, an RF antenna that is used to provide a communication link between a spacecraft and a ground station may use an RF antenna having a narrow signal radiation pattern so as to obtain longer signal reach in a specific direction between the spacecraft and the ground station.
The radiation characteristics of these various types of antenna may be evaluated in various ways. For example, in a first approach, a RF test antenna is configured to receive an RF signal from an RF antenna. The RF test antenna is used to detect a received signal strength at various locations and the results used to generate a radiation pattern that provides information pertaining to the radiation characteristics of the RF antenna.
In another traditional approach, a test instrument incorporating a bolometer may be used for testing an RF antenna. The bolometer operates on the principle of determining a signal strength of a received RF signal based on measuring a change in resistance in a detector element (a diode or a resistor, for example) as a result of heating of the detector element by the RF signal. The change in resistance can be measured by using a Wheatstone bridge that provides good sensitivity for measuring small changes in the amplitude of electrical current flowing through the detector element. The changes in amplitude of the electrical current flow is indicative of changes in signal strength of the received RF signal. Accordingly, the test instrument incorporating the bolometer can be used for testing RF signal strength at various locations and at various times as desired.
While traditional approaches such as the ones described above may be suitable for testing an antenna in a test chamber or for testing an antenna after the antenna is installed at a site, such types of testing may prove unsuitable for rapidly evaluating a batch of RF antennas in a manufacturing line, particularly when each RF antenna is located inside a device such as a smartphone, for example. It is therefore desirable to provide a system that can be used to evaluate a number of RF antennas rapidly in a pass-fail type of test for example. It may also be desirable that the test provide information not only pertaining to signal strength of a received RF signal but also additional information such as polarization characteristics of the received RF signal.